1. Field of the Invention
The present invention relates to a zoom lens system and an image taking apparatus including the zoom lens system, and more particularly, to a zoom lens system and an image taking apparatus including the zoom lens system, which are suitable for a video camera, a silver-halide camera, a digital camera, a TV camera, or a monitoring camera.
2. Description of the Related Art
In recent years, zoom lens systems having a small F-number (Fno), a wide field angle, a compact size, a high zoom ratio, and a high resolution are demanded as photographing optical systems for use in image taking apparatuses such as video cameras or digital still cameras, using a solid state image pickup element. Further, the zoom lens systems are demanded to provide an image stabilizing function for preventing a blur of a photographed image.
In order to satisfy all of the above-mentioned demands, the photographing optical system is increased in size, and the weight of the entire apparatus is increased. For example, when the optical component that performs image stabilization is increased in size, a drive section having a large drive force must be applied in order to operate the optical component, and the image stabilizing system including the drive section is increased in size to increase the weight of the entire apparatus. In addition, a response of an image stabilizing operation is deteriorated.
For the image stabilization, when a lens unit which is a part of the zoom lens system is moved in a direction perpendicular to an optical axis, a decentering aberration occurs, and hence optical performance is liable to be deteriorated.
Accordingly, it is important that, in the zoom lens system having an image stabilizing mechanism, the lens unit for lens stabilization is small in size and light in weight, and the deterioration of the optical performance due to image stabilization is low.
There is a zoom lens system including four lens units each having positive, negative, positive, and positive refractive powers which are arranged in order from an object side to an image side. There has been known the four-unit zoom lens systems in which the second and fourth lens units are moved during zooming, and a part of the lens units is moved to correct image blur. Among those zoom lens systems, there has been known zoom lens systems in which the third lens unit is divided into a lens unit having a negative refractive power and a lens unit having a positive refractive power, and the lens unit having a positive refractive power is moved in a direction perpendicular to the optical axis to correct the image blur (Japanese Patent Application Laid-Open No. H07-128619, U.S. Pat. No. 6,606,194, Japanese Patent Application Laid-Open No. 2002-244037, and Japanese Patent Application Laid-Open No. 2003-322795).